This invention relates to a process for thermal transfer impression and, more particularly, to a thermal transfer impression process in which an impressed image is transferred under application of heat from a thermal transfer ink roll to an image receiving substrate.
A thermal transfer recording system superior in archival quality, indelibility, or solvent resistance of the impressed record has recently begun to come into actual use to compete with the thermosensitive recording system employing a thermal recording device such as thermal printer or thermal facsimile. The so-called thermal transfer recording sheet used in said system comprises a support and a fusible ink layer disposed on one side of the support. In using the thermal transfer recording sheet, it is superposed upon a normal paper sheet so as to bring the ink layer in contact with the latter paper sheet, and, under application of heat from a thermal head such as that of a thermal facsimile, the ink is transferred from the thermal transfer recording sheet to the normal paper sheet to impress a record. In such a use of the thermal recording sheet, the proportion of the area necessary for the thermal transfer recording is extremely small compared with the total area of the sheet and, in addition, the thermal transfer recording sheet once used cannot be re-used, namely, the sheet is no more than a one-time sheet which is disadvantageous also from the standpoint of labor saving.
There are proposals regarding the process for preparing a master sheet for use in hectograph (master sheet for light printing work) capable of duplicating a large number of copies of the impressed image recorded by means of a thermal recording device similar to those described above. As examples, mention may be made of Japanese Patent Application "Kokai" (Laid-open) Nos. 28,892/81, 37,191/81, and 63,258/82. The Patent Application "Kokai" No. 28,892/81 discloses that both the impression by thermosensitive recording and the preparation of a master sheet for hectograph capable of duplicating a plurality of copies of the impressed record can be simultaneously achieved by arranging in order, under a thermosensitive recording sheet impressible with a heating element, a master image forming substrate sheet and a hectograph carbon paper with its thermosensitive transfer ink layer in contact with said substrate sheet. The Patent Application "Kokai" No. 37191/81 discloses that a master sheet for hectograph capable of duplicating a plurality of copies by impression with a heating element can be prepared by arranging under a master image forming substrate sheet a carbon paper for hectograph with its thermosensitive transfer ink layer in contact with said substrate sheet. It is described in the Patent Application "Kokai" No. 63,258/82 that a master sheet for office duplicating can be obtained by superposing a normal paper sheet on a transfer paper sheet comprising a paper sheet coated with an ink composed essentially of a color dye or a colorless leuco dye capable of forming color by reaction with an acidic color developer, a wax, and a binder, then thermally impressing on the side of said normal paper sheet to transfer the ink image to the normal paper sheet.
In the above proposals, it is intended to produce a master image by using a hectocarbon paper sheet or a transfer paper sheet and a thermosensitive recording device and to obtain a plurality of duplicated copies (prints) by using the resulting master sheet and a fluid duplicator (spirit press). The hectocarbon paper or the transfer paper is also a one-time type like the thermal transfer recording sheet previously mentioned. It is, moreover, a coated paper sheet comprising a base sheet coated with a composition to be transferred to a receiving substrate and, hence, requires coating operation in its production.
This invention further relates to a process for thermal transfer impression of the multicolor type. More particularly, it relates to a process for thermal transfer multicolor impression, in which an impressed image is transferred by applied heat from a thermal transfer ink roll to an image receiving substrate sheet. The thermal transfer recording in single color, e.g. black, has already been put into practice and the developmental effort has been shifted from monochrome to multicolor which has begun to come into actual use, as will be found also in various patent literature such as, for example, Japanese Patent Application "Kokai" (Laid-open) Nos. 182,488/82, 182,489/82, and 182,490/82. The Patent Application "Kokai" No. 182,488/82 discloses a thermal transfer sheet comprising a substrate sheet coated with a thermal transfer ink layer composed of portions of primary colors, red, blue and yellow, and one black ink portion for each set of three primary colors. In the Patent Application "Kokai" No. 182,489/82, the ink layer is composed of a set of different colors, each of which occupies an area which depends on the frequency of use of each color. In the Patent Application "Kokai" No. 182,490/82, a plurality of different colors are arranged along the secondary scanning direction. In using the thermal transfer recording sheets disclosed in the above patent documents, the sheet should be adjusted in accordance with the color to be transferred. For such registering purpose the recording unit and the driving unit for conveyance become complicated. Another disadvantage is the difficulty of increasing the speed of recording.
To solve the above problems, the present inventors carried out an extensive study and, as a result, achieved the invention of an impression process which permits thermal transfer by the application of heat using a thermal transfer ink roll.